Farzin Salmasi,
Volume 0, Issue 0 (8-2024)
Abstract
Sluice gates are commonly used to measure water discharge and to adjust the water level in open canals. Sluice gates can also be used at the crest of dam spillways for controlling floods. Estimation of head loss (∆E/E0) and discharge coefficients (Cd) for a sluice gate is essential for the design of open canals. Depending on the downstream water level, free or submerged flow conditions may occur. Although there have been some investigations on Cd for sluice gates, a comprehensive literature review shows that there are no studies of ∆E/E0 (to the best knowledge of the authors). Knowledge of ∆E/E0 is necessary for the design of intakes and irrigation canal inverts. This study uses the physical model of sluice gate to introduce helpful charts for energy loss estimation. Experiments were conducted in the University of Tabriz, department of water engineering. A rectangular canal with length of 12 m, width of 0.5 m and height of 0.8 m was used. Vertical slide gate was installed at the 6 m from canal inlet to permit flow become uniform. Water circulation is carried out using a submerged pump. Water is pumped in a 4.5 m head tank and then inters to canal with pipes. Water level/depth was measured with a point gauge with 0.1 mm accuracy. Discharge was measured with a calibrated rectangular sharp crested weir. Experiments were carried out with different discharges and gate opening. Results show that ∆E for free flow is greater than that for submerged flow conditions. Meanwhile, discharge coefficients in a free flow are greater than those under submerged flow conditions. Relative energy losses (∆E/E0) have a minimum value of 0.271 and a maximum value of 0.604. These high energy losses cannot be ignored in intake structures and canal-designing processes and their impact on minor canal inverts receiving water from main canals should be considered. The relative energy loss changed from the minimum value of 0.271 to the maximum value of 0.604. Multivariate regression method was used to calculate the relative energy loss and the average of the residuals was -0.004. The maximum and minimum residuals for ∆E/E0 are 5 and -0.31, respectively. A mathematical equation with a coefficient of determination of 0.925 was presented to separate the boundary of free flow from submerged flow. To estimate the discharge coefficient in submerged flow, a mathematical equation was obtained. For this equation, the average of the residuals was -0.004. The maximum and minimum residuals for the discharge coefficient are -0.084 and 0.116, respectively. Application of multiple non-linear regression (MNR) models are presented for predicting ∆E/E0 and Cd. The high energy losses cannot be ignored in intake structures and canal designing processes. Their impact on minor canal inverts receiving water from main canals should be considered. Application of MNR was presented from a simple equation to more sophisticated equations by improving regression relations in each step. The MNR method provides accurate equations for predicting performance for both ∆E and Cd.
Mohammad Hasan Hashemi Fesharaki, Ali Khoshfetrat, Elham Izadinia, Ehsan Delavari,
Volume 24, Issue 2 (6-2024)
Abstract
Dams are one of the best ways to store water in the long term. In general, it is important to increase the coefficient of water passage, more energy loss, and of course, to reduce scour downstream of dams and hydraulic structures and overflows. Weirs are part of hydraulic structures that allow more flow to pass over them during floods. Crump spillway also improves and protects the body of dams and spillway by passing excess flow during floods. Increasing the energy loss prevents the flow rate and scour or reduces the scour and prevents cracking and overturning of the crump weir. Many people have done valuable studies on the water transfer coefficient of crump weirs, but a review of previous research shows that few researchers have investigated the energy dissipation of crump weirs. Also, the energy dissipation in free flow and submerged states in Crump weirs has not been investigated. One of the conditions that can lead to an increase in energy loss is the presence of obstacles in the downstream slope of crump spillways. To better understand these cases, in this research, Crump spillways with different heights and slopes upstream and downstream were used. Also, the existence of the block (baffle) and the free and immersed states of the flow were investigated to estimate the energy losses. Experiments were carried out in a flume 10 meters long, 0.6 meters wide and 1.2 meters high. The flow is supplied by a pool tank and a pump. The flow is calmed down by flow relaxers and then reaches the overflow in 6 meters. To evaluate the effect of the slope and height of the spillway, three spillway models with a height of 0.15 meters and one spillway with a height of 0.2 meters and with different slopes upstream and downstream of the spillway were used. The flow rates used are 0.03, 0.035, 0.04, 0.045 and 0.05 cubic meters per second. By setting the appropriate engine speed for the pump, the flow rate entered the laboratory flume through the tank and the water depth was measured with the sensors installed on the top of the flume. The results showed that with the increase in the height of the overflows, the amount of energy loss decreases. The amount of energy loss in free flow mode with baffle is higher than the amount of energy loss in free flow mode without baffle. The amount of energy loss in submerged flow mode is lower than the amount of energy loss in free flow mode. As the downstream angle of the overflow decreases, the energy loss increases. By reducing the upstream angle of the overflow, energy loss is reduced. The amount of energy loss in free flow mode in type A, B, C and D spillways is 33.29, 33.83, 39.77 and 27.32% respectively. A general relationship was presented to calculate the amount of energy loss in crump weirs. In this relationship, there is a coefficient that is a function of free flow without baffle, submerged flow and free flow with baffle.
